Service observing system



Oct. 24, 1944. E. VAN DAMME 2,360,989

I SERVICE OBSERVING' SYSTEM Filed 001:. 29, 1942 Q I E I Q 8 l- I I 1:0;I I

lNl ENTOR LE. VAN DAMME BY v W ATTORNEK Patented Oct. 24, 1944 SERVICEOBSERVING SYSTEM Louis E. Van Damme, Weehawken, N. J assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application October 29, 1942, Serial No. 463,771

3 Claims.

This invention relates to telephone service observing systems and moreparticularly to systems for registering dial pulses transmitted by atelephone subscriber, to control central ofiice switching equipment, ofthe character originally described and claimed in United States Patent1,795,656 to R. F. Massonneau, issued March 10, 1931, and laterdescribed in Patent 2,017,644 to L. H. Allen et a1. issued October 15,1935, in which later patent as described on page 11, line 27, leftcolumn, a condenser 448 is referred to as connected between the grid andfilament of tube 424 for the purpose of preventing registration of splitimpulses, i. e., the registration of two short impulses instead of oneimpulse of normal length, which it may be explained is caused byoscillating transient voltages which appear during dialing on the ringconductor of the line under observation. Condenser 448 is of smallcapacity and tends to suppress or counteract excessive high peaks ofsuch oscillating pulsations and prevents the reoperation of the dialpulse responsive relay 408 during the interval the dial contacts areopened.

In certain recently developed systems, for example the so-calledautomatic ticketing system disclosed in a copending application, filedJune 27, 1942, in the name of F. B. Blake, Serial No. 448,753, thecalling subscribers line, after seizure by the line finder, is firstconnected to battery and ground through the conventional line relay (notshown) in the first selector I84, and later to battery and groundthrough a similar line relay 201, in the ticketing trunk (Fig. 2), bothof which relays (in practice) have two equal resist ance windings of 200ohms each.

Following the description of the progress of a call, the tip conductorof the calling line is connected to ground and the ring conductor tobattery in series with the middle winding of pulse responsive relay I000in the sender (Fig. 10) which connection serially includes a retardationcoil I00 I. In practice the middle winding of relay I000 is 190 ohms andthe retardation coil IBM has a resistance of 133 ohms or a totalresistance of 323 ohms between the ring conductor of the subscribersline and battery, as compared to the 200-ohm resistance of the lowerwinding of the preceding pulse or line relays, such as 201, andconsequently if We assume the grid of tube 424 of the pulse detectingand registering circuit, shown in the Allen et al. patent, is connectedto the ring conductor of the line over which pulses are beingtransmitted, to conductor I88 (Fig. 1) of the above-mentioned Blakeapplication, for

example the steady state potential of the grid of tube 424 will be lessnegative with respect to the filament when the dial contacts are closedand the calling line is connected to relay I000, than when the line isconnected to either of the preceding pulse relays such as 201, due tothe greater drop in potential due to the increase in resistance from 200to 323 ohms. Therefore, if the service observing system shown in theAllen et a1. patent, as previously referred to, is connected to a linewhich, in dialing a call, is routed through the automatic ticketingsystem disclosed in the Blake application, we have the condition wherethe grid of the tube 424 is, at one stage of the dialing, subject to acertain potential variation and at a later stage subject to a differentand wider variation, so, if the condenser between the grid and filamenthas the proper capacity so that the pulse relay responds properly underthe first condition, under the second condition it will fail to reach asteady state during dialing due to the greater potential variationbetween dial open and dial closure and therefore the pulse detectorrelay will respond sluggishly and may fail to properly record the dialpulses transmitted to the automatic ticketing sender,

It is obvious from the foregoing that for more universal use, acondenser connected between the grid and filament of the pulse detectortube, as previously used, is objectionable and must be removed to permitproperregistration when the observing circuit is connected to anautomatic ticketing system and hence a more suitable and satisfactorymeans for controlling the pulse detector relay is necessary which is theobject of the present invention, 1. e., to eliminate both split pulsesand false registration due to private branch exchange surges.

A feature of the invention resides in an improved arrangement wherebythe foregoing objects are attained.

The improved arrangement, according to the present invention, will bebest understood from the following description, when read in connectionwith the accompanying drawing which shows the pulse detecting andrecording portion of the observing system disclosed in the previouslymentioned Massonneau Patent 1,795,656 to which has been added, as shownin heavy line within the broken line box, means for preventing split andfalse pulse registrations regardless of variations in the potentialsafiecting the grid of the first detector tube at different stages ofdialing a connection.

It will be understood that in the arrangement disclosed in theMassonneau patent false operation and release of the pulse relay I2I,due to oscillating transients in the line circuit, was not recognizedand hence no means was suggested for correcting this trouble, but in theAllen et al. patent, as before referred to, a condenser is shownconnected between the grid and filament of the first tube 424(corresponding to tube II4 of Massonneau) which had for its purpose thecorrection of these troubles. This, however, as before described provedunsatisfactory when a more universal arrangement was required for usewith systems embodying automatic ticketing, hence the improvedarrangement hereinafter described.

Referring to the drawing, the reference numbers in the I series are thesame and indicate the same elements as shown and described in theMassonneau patent and the alphabet characters C, R, PLl, etc. indicatethe equipment which has been added to the Massonneau arrangement toachieve the objects of the present invention which added equipment isshown within a broken line box at the lower right-hand side of the draw-As in the Massonneau patent until the pulse recording equipment isconnected to a calling line, tubes I I4 and H8 are in a normallybalanced condition and'the armature of relay I2I remains on its backcontact.

When the equipment is connected to the line, before dialing begins, thegrid of tube I I4 is driven more positive due to the reduced negativepotential of the ring conductor of the line and the plate current oftube II4 increases thereby causing the armature of relay IZI to closeits front contact and connect ground to the upper winding of normallyoperated relay PL1 to cause this relay to release. This is due tocurrent flowing in the upper winding which is in a direction to overcomethe flux in the lower winding which causes the armature to be attracted.Opening of the front contact of relay PL1 releases magnet I24 and thepen is disengaged from the tape roller I25.

When the dial contacts are opened for the first pulse, the potential onthe grid of the tube H4 becomes more negative thus reducing the platecurrent and causing relay I2I to release to open its front contact,thereby removing ground from the upper winding of relay PL1 whereuponthis relay reoperates as soon as condenser C1 has become charged to thepotential of battery B1 in series with resistance R2 and the upperwinding of the relay.

When relay PLl operates, it energizes the pen register magnet I24 tocause the pen to engage the tape roller I25 thereby registering a dialimpulse, i. e., the opening of the dial contacts.

When the dial contacts close thereby ending the impulse, the grid oftube H4 again becomes more positive and increased plate current againflows thereby causing relay I 2I to operate to again connect ground tothe upper winding of relay PL1, thereby causing this relay to release,which in turn removes ground from the pen register magnet to permit thepen to be disengaged from the tape roller thereby registering areclosure of the dial contacts.

Condenser C1 which is charged when relay I2I released is nowshort-circuited in series with resistance R2 and discharges. It willthus be obvious that relay PLl is delayed in its reoperation, inresponse to opening of the dial contacts, and hence a surge impulsefollowing the reclosure of the dial contacts at the end of a series ofdigit pulses, which pulse is in a direction to momentarily drive thegrid of tube II4 more negative, and cause relay I2I to release, will beineffective to cause the pen to register a false extra pulse.

It will be noted that an auxiliary source of positive potential, batteryB (of the order of volts), is connected, in series with a highresistance R (of the order of 1 megohm), and a low capacity condenser C(of the order of .04 microfarad), to the grid of balancing tube H8, butwhen the recording equipment is connected to the line before dialingstarts, relay I2I will be operated thus short-circuiting this batterythrough the resistance R.

When relay I2I releases due to opening the contacts of the dial, theshort-circuit is removed from battery B and a surge of current flowsfrom its positive terminal in a circuit including resistance R,condenser C, high resistance R1 and resistances II! and H6 to thenegative terminal of the filament battery. The drop in potential acrossresistance R1 due to this current is such as to momentarily drive thegrid of tube II8 more positive with respect to the filament thusincreasing the plate current flowing in the middle winding of relay I2Iwhich increases the opposition to this relay operating and thereforeoscillating transient voltages present in the line during the intervalthe dial contacts are opened, which otherwise might tend to reoperaterelay I2! by increasing the current flowing in its right-hand winding,will be offset by the increased current flowing in its middle windingcaused by the surge of charging current through condenser C.

It will be evident from the foregoing that the arrangement of thepresent invention, as applied to the pulse recording system of theMassonneau patent, is effective to prevent the recording of split andextra false pulses without interfering with operation of the equipmentwhen observing on lines whose ring conductor may, at various stages of adialed connection, have different potentials when the dial contacts areclosed.

What is claimed is:

1. In a system for recording dial pulses, transmitted over a line by atelephone subscriber, to control automatic switches, which comprises apair of vacuum tubes, a differential relay having an individual windingincluded in the output circuit of each tube and adapted to operate andrelease in accordance with closures and openings of the dial contacts,and a mechanism controlled by the differential relay to graphicallyrecord the operated and released interval of said differential relay, inwhich system a potential surge may occur in the line following return ofthe dial to normal which is in a direction to momentarily release thedifferential relay and also in which oscillating transient potentialsoccur in the line each time the dial contacts are opened which potentialmay cause the differential relay to momentarily operate, characterizedby time delay means intermediate said differential relay and therecording mechanism to prevent recording a false dial pulse due to afalse momentary release of said differential relay, said delay me anscomprising a normally operated condenser-timed polar relay so arrangedand connected that it is released to deenergize said recording mechanismwhen the differential relay operates and to reoperate with apredetermined delay to energize said recording mechanism when thedifferential relay releases, and other means comprising a source of highpotential and a low capacity condenser serially connected to the grid ofone of said vacuum tubes and controlled by said differential relay formomentarily increasing the plate current in said tube and in one windingof the difierential relay, When that relay is released, to prevent itsimmediate reoperation due to an increase of current in its otherwinding.

2. In a system for recording dial pulses transmitted over a line by atelephone subscriber to control the pulse relay of an automatic exchangewhich comprises a vacuum tube having its input circuit connected inparallel with said pulse relay and a differential relay connected to itsoutput circuit which differential relay operates and releases inaccordance with the closures and openings of the subscribers dialcontacts to control a pulse recording mechanism, in which sys tem apotential surge immediately appears in the line each time the dialreturns to normal which surge is in a direction to cause thedifferential relay to momentarily release, thus falsely recording anextra pulse, characterized by time delay means comprising a normallyoperated condenser-timed polar relay intermediate said differentialrelay and recording mechanism adapted to deenergize said recordingmechanism when the differential relay is operated and to energize saidmechanism after a predetermined delay when the differential relayreleases.

3. In a system for recording dial pulses, transmitted over a line by atelephone subscriber to control automatic switches which comprises apair of vacuum tubes, a differential relay having an individual windingincluded in the output circuit of each tube and adapted to operate andrelease in accordance with closure and opening of the dial contacts anda mechanism controlled by the differential relay to graphically recordthe operated and released intervals of said differential relay, in whichsystem an oscillating transient potential appears in the line each timethe dial contacts are opened to cause the differential relay tomomentarily operate, characterized by means comprising a source of highpotential and a low capacity condenser serially connected to the grid ofone of said vacuum tubes and controlled by said difierential relay formomentarily increasing the plate current in said tube and in one windingof the differential relay, when that relay is released, to prevent itsimmediate reoperation due to an increase of current in its otherwinding.

LOUIS E. VAN DAMME.

